1. Field of the Invention
This invention relates to an angular velocity sensor, including support members, which are bonded to nodal points of a pillar-shaped oscillator, generated on oscillations thereof, and which may be used simultaneously for mechanically supporting and electrically connecting said oscillator.
This application claims priority of Japanese Patent Application No. 2003-351393, filed on Oct. 9, 2003, the entirety of which is incorporated by reference herein.
2. Description of Related Art
As angular velocity sensors for civil use, a so-called oscillation gyro type angular velocity sensor, in which bar-shaped oscillators are oscillated at a preset resonant frequency, and the Coriolis force, generated under the effect of the angular velocity, is detected by e.g. a piezoelectric device, to detect the angular angular velocity, is in wide-spread use.
In these angular velocity sensors, the oscillator shape maybe exemplified by a square pillar shaped vibrating reed. For supporting the vibrating reed, two nodal points of the oscillations may be supported by electrically conductive members.
FIG. 1 shows a method for supporting a conventional angular velocity sensor. In FIG. 1, a groove 95 is provided for extending longitudinally in a mid area along the width of a predetermined surface of an oscillator 96, formed of a piezoelectric material, thereby splitting the predetermined surface of the oscillator 96 into a surface area 91a and a surface area 91b. On the other hand, electrically conductive support members 40, 41 are mechanically and electrically connected to the oscillator 96 by connecting parts 40a, 41a, respectively. The connecting methods may be exemplified by solder connection or by electrically conductive adhesives.
With the above-described conventional angular velocity sensor, the oscillator 96 is oscillated by applying driving signals across the support members 40, 41. If the oscillator 96 is rotated about the longitudinal direction as an axis, the Coriolis force is generated, so that electrical signals of opposite polarities, proportionate to the Corilois force, are generated on the surface areas 91a, 91b of the oscillator 96. These electrical signals may be taken out from the support members 40 to detect angular angular velocity signals.
The support members 40, 41 must have two contradictory functions, that is, a function of restraining the nodal points of oscillation and a function of affording certain degree of freedom to the nodal points, in order to permit oscillations of the oscillator 96. If the restraint of the support members 40, 41 is strong, the amount of oscillations is decreased to lower the detection sensitivity for the angular velocity. If conversely the restraint is weak, the nodal points of oscillations are moved appreciably, thus presenting the problem of unstable characteristics.
If, with the recent tendency towards device size reduction, the support members 40, 41 are linear in shape, as shown in FIG. 1, the distance is shorter, as a matter of course, thus raising the twist resistance. Thus, such a technique is used which consists in bending the support members 50, 51 back and forth a plural number of times to lower the twist resitance, as shown in FIG. 2 (see, for example, Japanese Patent Publication H-10-332379).
On the other hand, an insert mold is used for securing a support member, in light of mass-producibility and cost reduction. With the insert mold, stationary positions of the upper and lower support members 50, 51 need to be shifted, because of the manufacture constraint, imposed on the insert mold. Thus, the upper and lower support members 50, 51 were necessarily arranged about the nodal points of the oscillation as axis.
However, in case the upper and lower support members 50, 51 are arranged symmetrically, as shown in FIG. 2, the space free of the support members in the vicinity of the oscillator 96 is decreased, thus worsening the assembly property, such as handling. This problem is felt more acutely as the device size is reduced.
On the other hand, if impact is applied from outside, the stress applied to the nodal points acts inversely at upper and lower points, because the upper and lower support members 50, 51 are arranged in the reverse directions, with the result that rotational moments are generated at the nodal points. Due to this rotational moment, there is raised a problem of destruction of the connection between the support members 50, 51 and the oscillator 96.